1. Field of the Invention
The invention relates to a plasma display unit, and more particularly to a circuit for controlling power in a plasma display unit to prevent overpower in the same.
2. Description of the Related Art
A color plasma display unit is generally controlled such that a brightness is raised when a display load is small, and a brightness is lowered when a display load is high, in order to accomplish both a high peak brightness and low power consumption.
Without such control as mentioned above, there would be caused a problem of very high power consumption when a display load is high, for instance, when a white is displayed in a screen at entirety at a maximum level.
As one of methods of controlling power consumption in a plasma display unit, there is known a method including the step of transmitting a brightness control signal to a plasma display unit independently of an input image signal, to thereby control power consumption in accordance with the brightness control signal.
However, this method is accompanied with a problem that if a brightness control signal having been input into a plasma display unit were not in a proper range, the plasma display unit might operate in a range beyond a safe operation range.
Hence, a plasma display unit has been required to have a function of protecting the plasma display unit from overpower, by which power is reduced, if power to be consumed corresponding to a brightness control signal is over rated power in a plasma display unit, and preferentially takes an external brightness control signal, if power to be consumed corresponding to a brightness control signal is within rated power.
As one of solutions for protecting a plasma display unit from overpower, those skilled in the art might suggest a method in which a power source current is detected, and a brightness is controlled in accordance with the detected power source current in order to prevent a over-current from running through a plasma display unit.
This method inevitably includes a feedback control, because a brightness is controlled after a power source current has been detected.
However, a feedback control is inevitably accompanied with control delay. Hence, some frames might instantaneously receive overpower, resulting in that a power source has to be designed to be able to withstand such an instantaneous overpower. As a result, the above-mentioned method causes a problem of an increase in burden in designing a plasma display unit.
For instance, Japanese Unexamined Patent Publication No. 1-193797 (A) has suggested a plasma display unit including a spontaneously light-emitting device and a drive circuit for driving the spontaneously light-emitting device, wherein the drive circuit includes first means for detecting a volume to be displayed in the spontaneously light-emitting device, and second means for suppressing an increase in the volume, based on an output signal transmitted from the first means.
Japanese Patent No. 2625220 (B2) has suggested an image display unit which adjusts a brightness of an image in a frame by means of a control circuit, wherein the control circuit divides a frame into a first period in which an image is to be displayed and which is comprised of a plurality of weighted sub-fields, and a second period in which a brightness is to be adjusted. A brightness of an image is controlled by varying a length of the second period in a frame without changing a weighting ratio among the plurality of sub-fields.
Japanese Patent No. 2900997 (B2) has suggested a method of controlling power consumption in a display unit, including the steps of measuring power consumption in a display unit, increasing a brightness in the display unit in accordance with the power consumption or decreasing a brightness at a rate different from a rate at which the brightness is increased, integrating the power consumption, and controlling a brightness in accordance with the thus integrated power consumption to thereby limit the power consumption below a target power.
Japanese Unexamined Patent Publication No. 2000-305514 (A) has suggested a plasma display panel including first means for detecting an average of input image signals, second means for controlling a brightness in accordance with a signal transmitted from the first means, and third means for driving a plasma display panel to display images in accordance with a signal transmitted from the second means. The plasma display panel makes it possible to make power consumption constant, even if the average of input image signals were varied.
Japanese Unexamined Patent Publication No. 2001-13921 (A) has suggested an apparatus for driving a plasma display panel including a plurality of cells arranged in a matrix. The apparatus displays images at an intermediate tone brightness by dividing a unit display period into a light-emitting period and a non-light-emitting period, and repeatedly turning the cells on only in the light-emitting period. The apparatus calculates average power consumption by adding an average picture level of the input image signal to power having been consumed in the non-light-emitting period, and controls power consumption of the plasma display panel in accordance with the average power consumption.
Japanese Unexamined Patent Publication No. 5-181430 (A) has suggested an apparatus for controlling a power source in a portable computer, including an AC adapter through which power is supplied, a rechargeable battery, a charging circuit for charging the battery, first means for determining whether the battery is charged, second means connected to the first means for storing the determination made by the first means, third means for reading the selection stored in the second means, and producing and transmitting a command indicative of what is read out, when the portable computer is turned on, and fourth means for controlling the charging circuit in accordance with the command.
Japanese Unexamined Patent Publication No. 11-282396 (A) has suggested a method of controlling power consumption in a display unit, including the steps of (a) calculating a load factor of a screen, based on display data transmitted to the display unit, (b) measuring power consumed in the display unit, and (c) controlling a brightness in the screen in accordance with both the load factor calculated in the step (a) and the power measured in the step (b).
However, the above-mentioned problems remain unsolved even in the above-mentioned publications.
In view of the above-mentioned problems in the conventional power controlling circuits in a plasma display unit, it is an object of the present invention to provide a power controlling circuit which is capable of accomplishing power control without delay, preventing instantaneous overpower, and significantly relaxing requirements to a power source.
In one aspect of the present invention, there is provided a circuit for controlling power in a plasma display unit, wherein the circuit adjusts a display brightness relative to an input image signal in accordance with an external control signal in the plasma display unit, and the circuit integrates image signal level in one frame of the input image signal, determines a maximum in the display brightness in accordance with the thus integrated image level, and selects the maximum, if a display brightness defined in accordance with the external control signal is greater than the maximum.
For instance, the circuit may select the display brightness defined in accordance with the external control signal, if the display brightness defined in accordance with the external control signal is not greater than the maximum.
There is further provided a circuit for controlling power in a plasma display unit, wherein the circuit adjusts a display brightness relative to an input image signal in accordance with an external control signal in the plasma display unit, the circuit determines a maximum in a maintenance pulse number, based on both a value obtained by integrating image signal level in one frame of an input image signal, and a temperature at a part of the plasma display unit which part radiates heat influencing an effective maintenance frequency, and the circuit selects the maximum, if a maintenance pulse number defined in accordance with the external control signal is greater than the maximum.
For instance, the circuit may select the maintenance pulse number defined in accordance with the external control signal, if the maintenance pulse number defined in accordance with the external control signal is not greater than the maximum.
There is further provided a circuit for controlling power in a plasma display unit, including (a) a first circuit which receives an average picture level (APL) signal generated by integrating portions for displaying images in image signals input into the plasma display unit, frame by frame, determines an upper limit of an effective maintenance frequency, allowable to the average picture level, and transmits a first signal indicative of the upper limit, and (b) a comparator which receives both the first signal and a control signal in accordance with which a display brightness is controlled, compares the control signal and the first signal to each other, selects one of them which presents a smaller effective maintenance frequency, and outputs the thus selected signal as a signal used for controlling a brightness in the plasma display unit.
There is further provided a circuit for controlling power in a plasma display unit, including (a) a thermal sensor which detects a temperature at a part of the plasma display unit which part radiates heat influencing an effective maintenance frequency, and transmits a first signal indicative of the temperature, (b) a first circuit which receives both the first signal and an average picture level (APL) signal generated by integrating portions for displaying images in image signals input into the plasma display unit, frame by frame, determines an allowable upper limit of an effective maintenance frequency, based on both the average picture level and the first signal, and transmits a second signal indicative of the allowable upper limit, and (c) a comparator which receives both the second signal and a control signal in accordance with which a display brightness is controlled, compares the control signal and the second signal to each other, selects one of them which presents a smaller effective maintenance frequency, and outputs the thus selected signal as a signal used for controlling a brightness in the plasma display unit.
There is further provided a circuit for controlling power in a plasma display unit, including (a) a plurality of thermal sensors each of which detects a temperature at a part of the plasma display unit which part radiates heat influencing an effective maintenance frequency; and transmits a first signal indicative of the temperature, (b) a first circuit which receives both the first signals and an average picture level (APL) signal generated by integrating portions for displaying images in image signals input into the plasma display unit, frame by frame, selects a maximum temperature among temperatures indicated by the first signals, determines an allowable upper limit of an effective maintenance frequency, based on both the average picture level and the maximum temperature, and transmits a second signal indicative of the allowable upper limit, and (c) a comparator which receives both the second signal and a control signal in accordance with which a display brightness is controlled, compares the control signal and the second signal to each other, selects one of them which presents a smaller effective maintenance frequency, and outputs the thus selected signal as a signal used for controlling a brightness in the plasma display unit.
In another aspect of the present invention, there is provided a plasma display unit including any one of the above-mentioned circuits for controlling power in the plasma display unit.
In still another aspect of the present invention, there is provided a method of controlling power in a plasma display unit which is capable of adjusting a display brightness relative to an input image signal in accordance with an external control signal, the method including the steps of (a) integrating image signal level in one frame of the input image signal, and determining a maximum in the display brightness in accordance with the thus integrated image level, (b) comparing the maximum and a display brightness defined in accordance with the external control signal, and (c) selecting the maximum, if the display brightness defined in accordance with the external control signal is greater than the maximum, and selecting the display brightness defined in accordance with the external control signal, if the display brightness defined in accordance with the external control signal is not greater than the maximum.
There is further provided a method of controlling power in a plasma display unit which is capable of adjusting a display brightness relative to an input image signal in accordance with an external control signal, the method including the steps of (a) determining a maximum in a maintenance pulse number, based on both a value obtained by integrating image signal level in one frame of an input image signal, and a temperature at a part of the plasma display unit which part radiates heat influencing an effective maintenance frequency, (b) comparing the maximum and a maintenance pulse number defined in accordance with the external control signal to each other, and (c) selecting the maximum, if the maintenance pulse number defined in accordance with the external control signal is greater than the maximum, and selecting the display brightness defined in accordance with the external control signal, if the maintenance pulse number defined in accordance with the external control signal is not greater than the maximum.
There is further provided a method of controlling power in a plasma display unit which is capable of adjusting a display brightness relative to an input image signal in accordance with an external control signal, the method including the steps of (a) detecting temperatures at parts of the plasma display unit which parts radiate heat influencing an effective maintenance frequency, (b) selecting a maximum temperature among the temperatures, (c) determining a maximum in a maintenance pulse number, based on both a value obtained by integrating image signal level in one frame of an input image signal, and the maximum temperature, (d) comparing the maximum and a maintenance pulse number defined in accordance with the external control signal to each other, and (e) selecting the maximum, if the maintenance pulse number defined in accordance with the external control signal is greater than the maximum, and selecting the display brightness defined in accordance with the external control signal, if the maintenance pulse number defined in accordance with the external control signal is not greater than the maximum.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
In accordance with the present invention, even if an inaccurate brightness control signal is input into a plasma display unit, it would be possible to limit power consumed in a plasma display unit into an allowable range to be followed for ensuring safety in operation. In other words, it would be possible to avoid power to be consumed in a plasma display unit from becoming excessive power.
In addition, since the present invention can accomplish power control without delay relative to fluctuation in an image signal, it would be possible to prevent instantaneous overpower caused by control delay.
Furthermore, it would be possible to accomplish optimal power control, taking into consideration a part or parts of a plasma display unit which part or parts radiate(s) heat much influencing an effective maintenance frequency.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.